Fermentations take place in defined liquid media. These media will typically include various macro- and micro-nutrient sources that are important in improving fermentation performance. Media used in connection with less common substrates, such as gaseous substrates, require well defined media to optimize performance. Anaerobic fermentations also require well defined media.
Anaerobic microorganisms can produce ethanol from carbon monoxide (CO) through fermentation of gaseous substrates. Fermentations using anaerobic microorganisms from the genus Clostridium produce ethanol and other useful products. For example, U.S. Pat. No. 5,173,429 describes Clostridium ljungdahlii ATCC No. 49587, an anaerobic microorganism that produces ethanol and acetate from synthesis gas. U.S. Pat. No. 5,807,722 describes a method and apparatus for converting waste gases into organic acids and alcohols using Clostridium ljungdahlii ATCC No. 55380. U.S. Pat. No. 6,136,577 describes a method and apparatus for converting waste gases into ethanol using Clostridium ljungdahlii ATCC No. 55988 and 55989.
U.S. Pat. No. 7,285,402 describes media known for use in anaerobic fermentation of gaseous substrates to produce ethanol. Various component and component concentrations in the medium are effective for providing high levels of ethanol productivity. Eliminating certain components and reducing required concentrations levels of other components while maintaining ethanol productivity may provide significant cost savings, especially at a commercial scale fermentation.
The Wood-Ljungdahl pathway is well known in the art and includes reactions which can be separated into two branches: (1) methyl branch and (2) carbonyl branch. The methyl branch converts syngas to methyl-tetrahydrofolate (methyl-THF) whereas the carbonyl branch converts methyl-THF to acetyl-CoA. Acetyl-CoA may then be converted to ethanol. Enzymes catalyze reactions in the Wood-Ljundahl pathway and those enzyme require various elements for optimal functionality. For example, formate dehydrogenase, an important enzyme in the Wood-Ljungdahl pathway, requires selenium for optimal activity.